iOS开发之block

iOS开发之block

1.什么是block，block的作用

block      代码块，解决回调，理解为“匿名函数”，定义在方法里面（先定义，再使用）

2.block的基本使用（语法）

3.block在开发中的应用

在A、B两个界面之间传值，改变背景颜色

A界面

#import "SecondViewController.h"

@interface SecondViewController ()
{
    //定义block变量，为了保存传人的参数
    void (^_action)(NSString *color);
}
@end

@implementation SecondViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    self.view.backgroundColor = [UIColor brownColor];
    
    UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
    button.frame = CGRectMake(100, 200, 100, 30);
    [button setTitle:@"切换" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(btnClick:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
    
    
}
-(void)btnClick:(UIButton *)button
{
    
    if (_action) {
        _action(@"blue");
    }
    [self dismissViewControllerAnimated:YES completion:nil];
}
-(void)setChangeBackgroundColor:(void (^)(NSString *))action
{
    _action = action;
}

B界面

-(void)createView
{
    UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
    button.frame = CGRectMake(100, 200, 100, 30);
    [button setTitle:@"切换" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(btnClick:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
    
    
}
-(void)btnClick:(UIButton *)button
{
    
    
    
    SecondViewController *svc = [[SecondViewController alloc] init];
    
    [svc setChangeBackgroundColor:^(NSString *color) {
        if ([color isEqualToString:@"blue"]) {
            self.view.backgroundColor = [UIColor blueColor];
        }
    }];
    
    [self presentViewController:svc animated:YES completion:nil];
}